This invention relates to a fluid conducting system and more particularly to a system for conducting fluid, without mechanical connections, between components of a nuclear reactor that are capable of movement relative to each other.
In nuclear reactors, there has been a problem with conducting fluids across the interface between rotatable components. The problem consists of providing a linkage from one rotatable component to another so that a fluid may be passed across the interface of the rotatable components without the linkage interfering with the movement of the components. Although this problem arises in many different reactor applications, it has been particularly troublesome where rotatable plugs are used on the head of a reactor vessel for the purpose of refueling the reactor and sealing the reactor internals in the reactor vessel.
In nuclear reactor designs, well known in the art, a reactor vessel with fuel assemblies disposed therein, and having an inlet and outlet for circulation of a coolant in heat transfer relationship with the fuel assemblies, is sealed by a head located on top of the reactor vessel. In certain designs, the head comprises one or more rotatable plugs. These plugs, which may be of varying sizes disposed eccentrically within each other, serve at least two purposes. One purpose is, of course, to seal the reactor internals inside the reactor vessel. Another purpose is to support refueling machines. The rotation of the rotatable plugs positions the refueling machines in appropriate relationship to the fuel assemblies in the reactor vessel to facilitate the refueling process. Since the rotatable plugs must be able to rotate relative to each other, the plugs are mounted so as to define an annulus between them. This annulus, while allowing the rotation of the plugs, also provides a path for the release of radioactive particles located in the reactor vessel. Accordingly, seals are provided at various locations across the annulus to prevent this release of radioactive particles. Although these designs are effective designs from a refueling standpoint, they create a problem where it becomes necessary to conduct a fluid across the annular interface of the plugs.
It is well known to those skilled in the art, that there are at least two purposes for conducting a fluid across these annular interfaces. One such reason is that some of the seals located across the annular interfaces may need to be inflated or buffered with a gas such as argon. In addition, it may become necessary to purge the annuli with a purge gas such as argon to reduce the concentration of radioactive particles therein. In either of these applications, it is necessary to conduct a gas from a stationary supply to a series of rotatable plugs which necessitates conducting the gas across the annular interfaces. A number of methods have been devised for accomplishing this conducting of gas, but they have all involved mechanical connections between the plugs which complicates the apparatus used to rotate the plugs.
An example of the mechanical connections used to conduct a gas across the annular interfaces and still allow rotation of the plugs is the use of swivel joints on standard tubing or piping. Another method is to hang flexible tubing from a tubing handling device located above the reactor vessel head. However, both of these methods like the others known in the art greatly increase the complexity of the reactor vessel head area by adding additional equipment that hampers plug rotation and obstructs access to the head itself.
A typical example of the design of nuclear reactors which utilize rotatable plugs as part of the reactor vessel head and which may incorporate a gas purge of the annulus in the absence of an inner head seal is described in U.S. Pat. No. 3,522,144 -- J. Webb et al, issued July 28, 1970. The Webb patent illustrates the use of two liquid dip seals as the means for sealing the annulus to prevent release of radioactive particles. In this design, one of the liquid dip seals is located in the annulus near the top of the head while the other is located in the annulus near the bottom of the head. Under certain circumstances, radioactive particles present in a gas which covers the reactor coolant may bubble through the inner dip seal thus contaminating the annulus between the two dip seals. To minimize this contamination and to minimize the leakages of these particles through the outer dip seal, a gas such as argon or nitrogen may be introduced into the annulus between these dip seals building a pressure therein. The gas, under pressure, will bubble through the inner dip seal into the cover gas area of the reactor vessel thus reversing the leakage path and minimizing the escape of radioactive particles. Likewise, in the absence of the inner seal, the gas may be used to simply purge the annulus. While the Webb patent describes the use of a purge gas it does not teach a method of conducting the gas to several annuli in series. Therefore, the Webb Patent does not solve the problem of conducting a gas, without the use of mechanical connections, between the two components capable of relative movement.
In U.S. Pat. No. 3,819,479 -- R. Jacquelin, issued June 25, 1974, there is described an apparatus for conducting a gas to seals and annuli between two components capable of relative movement. The Jacquelin patent describes the use of ducts for piping the gas to the annulus, but it does not teach a method for conducting the gas across the annulus.